1. Field of the Invention
The present invention relates to a drive train for an electric car and, more particularly to a drive train for an electric car in which a motor is combined with a transaxle for transmitting the power of the motor to the vehicle drive wheels.
2. Related Art
One drive train used in electric cars is a triple shaft type drive system in which a motor shaft is arranged on a first axis, a counter gear shaft on a second axis and the output shaft (hereinafter referred to as a "drive shaft") of a differential gear unit on a third axis, so that the motor and the transaxle may be combined to transmit the power of the motor to the differential gear unit through a counter gear mechanism acting as a reduction gear unit, to thereby drive the wheel axle shafts joined thereto. The drive train of this type, in which the motor is combined with a transaxle, requires universal joints having a relatively large radial dimension arranged adjacent to the left and right sides of the differential gear unit. Such a drive train requires provision for avoiding interference between the motor and the large universal joints, which makes it difficult to shorten the distance between the axes of the motor shaft and the drive shaft. As a result, the drive train is longer than a drive train in which the motor and the differential gear unit are horizontally juxtaposed.
In an electric car, as in a car with an internal combustion engine, it is important to retain a sufficient shock absorbing space in the front end of the vehicle, in which the drive system is mounted, that is, in the engine (or motor) compartment, and, accordingly, a need exists to make the length of the drive train as short as possible. U.S. Pat. No. 5,295,413 exemplifies structure designed to meet the demand for a shortened drive train. The disclosed structure has the motor and the differential gear unit arranged vertically on opposite sides of the counter gear mechanism.
However, in the case of the prior art described above, it is necessary not only to avoid the interference between the motor and the universal joint but also to provide space for the structure accommodating the vertical motion of the axle shaft, so that the distance between the axes of the motor shaft and the drive shaft must be longer than that of a horizontal arrangement, thereby requiring enlargement of the vertical dimension of the drive system. Thus, a drive train having the motor and the differential gear unit vertically arranged makes it difficult to retain the minimum ground clearance if the level of the motor compartment of the vehicle is lowered to provide the needed increase in the vertical dimension.